2 What are enzymes?enzymes are proteins that function as biological catalystsa catalysts is a substance that usually speeds up the rate of a chemical reaction and is not changed by the reactionthus enzymes speed up the rate of metabolic reactions in the cells
3 Enzymes workenzymes lower the minimum amount of energy required for chemical reaction to occur (activation energy)this allows biochemical reactions to take place at a faster rate in the cells of living organisms at body temperature which is usually lowenzymes catalyse metabolic reactions (i.e. chemical reactions that sustain life) in a cellsmetabolic reactions are either breakdown reactions - catabolism or build up reactions - anabolism
4 Naming of EnzymesEnzyme are named according to the reaction they catalyseA suffix – ase is usually added to the name of the substrate of the reaction catalysed by the enzymeSometimes they are given special names such as catalase & amylaseCatalase is the fastest acting enzyme
6 “Lock and Key” ModelEach enzyme has a shape that allows it to catalyse one reactionReactant(s) in an enzyme – catalysed reaction is/are called substrate(s)Enzyme’s molecule has a specific shape which is complementary to that of a substrate –this is called active siteThe substrate fits into the active site of the enzyme the same way a ‘key fits into a lock’ - this is called “ lock and key” modelThe substrate (the ‘key’) fits exactly into the active site (the ‘key hole’) of the enzyme (the ‘lock’)An enzyme-substrate complex is formed.The substrate undergoes a chemical change – a new substance, the product, is formedThe product is released from the active site.The free unaltered active site is ready to receive fresh substrate.
8 General Properties of Enzymes enzymes are all Proteinsenzymes are Specific in reaction they catalyseenzymes are not changed by the reaction they catalyse i.e. they can be used again and againenzymes are influenced by change in temperatureenzymes are influenced by change in pHenzymes work best at particular temperature (37 oC in humans)and pH (pH 2 for pepsin & pH 7 for most enzymes)
9 Factors Affecting Enzyme Activity Enzyme activity is determined by measuring the rate of reaction that the enzyme catalysesThis is usually measured by measuring the products formed per unit timeEnzyme activity is affected by;temperature,pH &substrate concentration
10 Effect of Temperature on Enzymes at low temperature (e.g. 0°C) enzyme activity is low because the movement of molecules is slow due to low kinetic energythe collision frequency between enzyme and substrate is therefore lowincreasing the temperature, increases kinetic energy of molecules thus speeding up their movement, collision frequency between the substrates and the enzymes increases therefore enzyme activity increasesmaximum enzyme activity is at 40°C – due to maximum collision frequency between enzymes and substrates molecules – this is called optimum temperature (i.e. the temperature at which the enzyme works fastest)enzyme action decreases above 40°C because the enzymes are denatured by excess temperature (i.e. the shape of active site is altered & substrates molecules can no longer fit into it)when all the enzymes are denatured, at 60°C, enzyme activity stops
11 Effect of pH on Enzymesenzyme activity is greatest within a narrow range of pH, since all the enzymes are functioning normally because their active sites have the correct shapethis is called the optimum pHchange in pH from the optimum, alters the shape of active site thus affecting the ability of the substrates to bind to the active site & so enzyme activity decreasesa major change in pH from the optimum denatures the enzymes so enzyme action stopsWhat is the optimum pH for;enzyme X?enzyme Y?
12 Revision activityAfter reading pages of your biology textbook and your lesson notes, attempt summary Questions 1, 4, 5, 7, & 6 on page 42.